The NAADSM model specification

The NAADSM model specification is intended to be a plain-language description of the conceptual model implemented in NAADSM. Its purposes are to facilitate agreement among current team members on details of the model, to provide a basis for functional testing, and to provide future team members and other users with a complete but accessible description of the model.

For historical reasons, NAADSM version numbers start at 3.0.0. This scheme reflects continuity with SpreadModel1, the conceptual model on which NAADSM was originally based. Version numbers for the NAADSM specification document start at 1.0.0: the first version of the NAADSM specification document was written for NAADSM 3.0.0. For a more thorough description of NAADSM version numbers, please see NAADSM versioning.

Development of NAADSM is on-going, and new versions of the program are written to conform to updated versions of the model specification. The model specification is updated via Requests for Comment (RFCs). RFCs provide detailed descriptions of proposed changes to the model specification. RFCs should include justification for the proposed changes and any supporting documents, e.g., manuscripts from the scientific literature. Changes proposed in RFCs are discussed and may be revised by the NAADSM Development Team. An RFC that is accepted after evaluation is merged into a new version of the model specification.

The following tables show the relationships between versions of the NAADSM application and the model specification, and list RFCs that have been incorporated in the specification document.

Specification 2.0 (for NAADSM 4.0)

NAADSM 4.0 is the first new major release of NAADSM since its introduction in 2006. This version addresses several deficiences identified in previous versions. Among the most notable differences between NAADSM 4.0 and NAADSM 3.x are the following:

Local-area spread is implemented as a mechanism of disease transmission separate from long-distance airborne spread

The formulas used for local-area and airborne spread have been fully revised, so that these parameters are more epidemiologically and mathematically plausible

A more refined approach to simulating the effect of within-unit prevalence of disease on transmission by direct, local-area, and airborne spread is implemented

Unlike previous releases, NAADSM 4.0 is not fully backward compatible with previous versions. Scenarios developed for NAADSM 3.x must be adapted to run with NAADSM 4.0.

Replacing the algorithm for airborne spread: This RFC proposes the separation of local-area from airborne spread, and alters the formula used to calculate the probabilities of disease transmission by these two mechanisms.

Within-unit prevalence and disease spread by direct contact or local-area spread: This RFC introduces new parameters to more appropriately model the spread of disese by direct contact, local-area spread, and airborne transmission when the option to specify within-unit prevalence is used.

Elimination of delay parameters: This RFC proposes the elimination of rarely used and problematic parameters for delay in the effect of disease exposure by direct contact, indirect contact, and airborne/local-area spread.

Vaccination queues: This RFC describes a change in the behavior of the model to prevent units that require vaccination from being listed and counted in the vaccination queue multiple times.

Specification 1.2 (for NAADSM 3.2)

This version of NAADSM will allow tracing back from detected units. NAADSM 3.2 will be backward compatible with previous versions: scenarios developed for NAADSM 3.0 or 3.1 will run in NAADSM 3.2 without modification.

New distance formula: This RFC proposes a change to the way distances are calculated in NAADSM. A cartographic projection is applied to to latitude/longitude data to simply the calculation of distances between units. These changes are proposed for NAADSM 3.2.

Vaccination of detected, infected units:This RFC proposes a change to the way detected infected units are currently handled when vaccination is used as a disease control strategy. These changes are proposed for NAADSM 3.2.

Trace in:This RFC proposes a trace-in feature and an ability to do traces that go more than one step. Trace-in is part of the minimum required response to foot-and-mouth disease in the EU directive on FMD. These changes are proposed for NAADSM 3.2.

Specification 1.1 (for NAADSM 3.1)

This version of NAADSM introduced the option to simulate zones for disease detection and control. NAADSM 3.1 is fully backward compatible with version 3.0: scenarios developed for NAADSM 3.0 will run in NAADSM 3.1 without modification.

Specification 1.0 (for NAADSM 3.0)

NAADSM 3.0 was the first version developed and released by the international NAADSM Development Team. This version of the model is described by version 1.0 of the NAADSM specification as well as in a paper (Harvey et al. 2007) published in the journal Preventive Veterinary Medicine.

Note: The features of NAADSM 3.0 are a subset of those available in NAADSM 3.1. Scenarios developed for NAADSM 3.0 will run in NAADSM 3.1 without modification. Use of NAADSM 3.1 rather than NAADSM 3.0 is highly recommended.

Quarantine: This RFC proposes adding notes for clarification to the direct contact section about potential recipients that are quarantined, about distance limits for shipments, and about the conditions under which a shipment can be dropped.

Vaccination parameters for individual production types: This RFC describes the approach to vaccination used in legacy versions of SpreadModel, and proposes that it should be implemented in the current version of the model.